Conventional scanners process packages by reading and decoding information affixed to the packages as they move along a conveyor system. Typically, the scanners incorporate a light source and a light detecting means, such as charge-coupled device (CCD) sensors or complementary metal-oxide-semiconductor (CMOS) sensors. A portion of the light which is reflected from the package is detected by the image sensor and converted into an electrical signal, which is the basis for the object properties that include digital images of a package that has been read by the scanner. The digital image is processed and decoded according to instructions executed by one or more computer processors of the conventional scanners or the conveyor system.
The conventional scanners are manufactured with a high speed imager having a fixed focal length lens and a moving mechanical focus mechanism. The focus mechanism is positioned based on the dimension information of the package received from a rangefinder upstream from the scanner. The moving focus mechanism of the scanner is relatively slow, expensive, and can be a potential reliability problem. In instances when the scanner is unable to capture a useable image of the package, the packages are scanned manually by a package handler with a conventional scanner. The manual processing of the packages reduces the efficiency for package processing in the conveyor system.
Because of the limited depth of field associated with the fixed lens system, conventional scanners rely on the mechanical focusing mechanism to improve image quality. Normally, the depth of field is not large enough to produce sharp images for different types of package that vary in size (e.g., tall packages: boxes, and short packages: letters) on the same conveyor belt. Accordingly, pre-sorting by the package handlers may be employed during package processing. For instance, pre-sorting may require specific placement of packages based on package size or type. Alternatively, pre-sorting may require singulated flow of packages before packages are scanned.